1. Field of the Invention
The present invention relates to resinous polyols which are particularly useful in high solids coating compositions. More specifically, the present invention relates to high solids polyester polyols which are prepared by reacting low molecular weight polyols with polycarboxylic acids or functional equivalents thereof, wherein the reaction product is characterized by the presence of a significant amount of unreacted starting polyols.
2. Brief Description of the Prior Art
In preparing resinous polyols, particularly low molecular weight ones, the full implications of using a large excess of starting low molecular weight simple polyols had not been appreciated in the art. Certainly, the significance of using a large excess of starting polyols, followed by removing a substantial portion of the attendant unreacted starting polyols from reaction products had not been appreciated in the art. Specifically, it had not been appreciated that by removing unreacted starting polyols, performance properties of coating compositions comprising the resultant resinous polyol could be affected significantly.
In the prior art preparation of low molecular weight resinous polyols, there are employed controlled amounts of starting polyols. The amounts of starting polyols are controlled in such a manner as would produce resinous polyols containing tolerable amounts of unreacted starting polyols. Usually, unreacted starting polyols in these amounts, i.e., up to about 5 percent, are not considered detrimental and therefore are not intentionally removed from the reaction product.
In the somewhat related areas of preparing high molecular weight resins, low molecular weight polyols are sometimes removed as by-products of the polymerization process. The intent or effect of removing the polyols is quite different from that of the present invention. In these areas, removal of polyols is necessary to obtain the desired high molecular weight products. For example, in preparing high molecular weight polyesters for fiber manufacture, low molecular weight polyester polyols are made to undergo transesterification reaction. This results in an increase in molecular weight and is accompanied by formation of low molecular weight polyols as by-products. Removal of the low molecular weight polyol by-products from the reaction mixture is critical to the formation of the high molecular weight polyesters. In other areas of preparing high molecular weight polyester polyols, polyols can be removed as a corrective measure, with a consequential molecular weight increase in the resultant polyester polyol.
In the present invention, starting polyols can be employed in relatively large excess with the intent of substantially increasing the low molecular weight and narrow molecular weight distribution of the resultant resinous polyols. While the reaction product is attended by a significant amount of unreacted starting polyol, a portion or all of the unreacted starting polyol can be subsequently removed from the reaction product. Thus, the low molecular weight and narrow molecular weight distribution of the resinous polyol is optimized.